Chloramines are strongly hemolytic and therefore are highly toxic to hemodialysis patients. Purified water for dialysis should not contain more than 0.1 ppm of chloramines. Presently, there is not a test available for the direct measurement of chloramines. Rather, the level of chloramines is obtained by calculation of the difference between the total chlorine and free chlorine levels. The overall goal of this project is to develop a two-step on-site test system which will be capable of measuring chloramines directly. In the first step, a specific, solid-phase reagent will be used to scavenge free chlorine (hypochlorous acid) from the sample. In the second step, chloramines will be detected by reaction with chromogenic reagents. Any color developed in the second step will be free of interference by free chlorine and will be a direct measure of chloramine levels. The sensitivity of the chloramine detection step will be increased by immobilizing the reagent(s) in a porous matrix through which large volumes of sample can be passed.